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SSA (computing)
In compiler design, static single assignment form (often abbreviated as SSA form or simply SSA) is a property of an intermediate representation (IR) that requires each variable to be assigned exactly once and defined before it is used. Existing variables in the original IR are split into ''versions'', new variables typically indicated by the original name with a subscript in textbooks, so that every definition gets its own version. In SSA form, use-def chains are explicit and each contains a single element. SSA was proposed by Barry K. Rosen, Mark N. Wegman, and F. Kenneth Zadeck in 1988. Ron Cytron, Jeanne Ferrante and the previous three researchers at IBM developed an algorithm that can compute the SSA form efficiently. One can expect to find SSA in a compiler for Fortran, C or C++, whereas in functional language compilers, such as those for Scheme and ML, continuation-passing style (CPS) is generally used. SSA is formally equivalent to a well-behaved subset of CPS excludi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Compiler
In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that translate source code from a high-level programming language to a low-level programming language (e.g. assembly language, object code, or machine code) to create an executable program. Compilers: Principles, Techniques, and Tools by Alfred V. Aho, Ravi Sethi, Jeffrey D. Ullman - Second Edition, 2007 There are many different types of compilers which produce output in different useful forms. A ''cross-compiler'' produces code for a different CPU or operating system than the one on which the cross-compiler itself runs. A ''bootstrap compiler'' is often a temporary compiler, used for compiling a more permanent or better optimised compiler for a language. Related software include, a program that translates from a low-level language to a h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Compiler Optimization
In computing, an optimizing compiler is a compiler that tries to minimize or maximize some attributes of an executable computer program. Common requirements are to minimize a program's execution time, memory footprint, storage size, and power consumption (the last three being popular for portable computers). Compiler optimization is generally implemented using a sequence of ''optimizing transformations'', algorithms which take a program and transform it to produce a semantically equivalent output program that uses fewer resources or executes faster. It has been shown that some code optimization problems are NP-complete, or even undecidable. In practice, factors such as the programmer's willingness to wait for the compiler to complete its task place upper limits on the optimizations that a compiler might provide. Optimization is generally a very CPU- and memory-intensive process. In the past, computer memory limitations were also a major factor in limiting which optimizations co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dominator (graph Theory)
In computer science, a node of a control-flow graph dominates a node if every path from the ''entry node'' to must go through . Notationally, this is written as (or sometimes ). By definition, every node dominates itself. There are a number of related concepts: * A node ''strictly dominates'' a node if dominates and does not equal . * The ''immediate dominator'' or idom of a node is the unique node that strictly dominates but does not strictly dominate any other node that strictly dominates . Every node, except the entry node, has an immediate dominator. * The ''dominance frontier'' of a node is the set of all nodes such that dominates an immediate predecessor of , but does not strictly dominate . It is the set of nodes where 's dominance stops. * A ''dominator tree'' is a tree where each node's children are those nodes it immediately dominates. The start node is the root of the tree. History Dominance was first introduced by Reese T. Prosser in a 1959 paper ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wide-issue
A wide-issue architecture is a computer processor that issues more than one instruction per clock cycle. They can be considered in three broad types: * Statically-scheduled superscalar architectures execute instructions in the order presented; the hardware logic determines which instructions are ready and safe to dispatch on each clock cycle. * VLIW architectures rely on the programming software (compiler) to determine which instructions to dispatch on a given clock cycle. * Dynamically-scheduled superscalar architectures execute instructions in an order that gives the same result as the order presented; the hardware logic determines which instructions are ready and safe to dispatch on each clock cycle. See also *Out-of-order execution *Explicitly parallel instruction computing Explicitly parallel instruction computing (EPIC) is a term coined in 1997 by the HP–Intel alliance to describe a computing paradigm that researchers had been investigating since the early 1980s. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Register Allocation
In compiler optimization, register allocation is the process of assigning local automatic variables and expression results to a limited number of processor registers. Register allocation can happen over a basic block (''local register allocation''), over a whole function/ procedure (''global register allocation''), or across function boundaries traversed via call-graph (''interprocedural register allocation''). When done per function/procedure the calling convention may require insertion of save/restore around each call-site. Context Principle {, class="wikitable floatright" , + Different number of scalar registers in the most common architectures , - ! Architecture ! scope="col" , 32 bits ! scope="col" , 64 bits , - ! scope="row" , ARM , 15 , 31 , - ! scope="row" , Intel x86 , 8 , 16 , - ! scope="row" , MIPS , 32 , 32 , - ! scope="row" , POWER/PowerPC , 32 , 32 , - ! scope="row" , RISC-V , 16/32 , 32 , - ! scope="row" , SP ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SSA Example1
SSA may refer to: Geography * Sub-Saharan Africa Organizations * Safe Schools Alliance, a British advocacy group * SSA Global Technologies, American software company acquired by Infor Global Solutions * Shan State Army, a former insurgent group in Burma * Slovak Society of Actuaries ( sk, Slovenská spoločnosť aktuárov), professional association in Slovakia * Soaring Society of America, American sporting society founded in 1932 * Society of Scottish Artists, artists society founded in 1891 * Swedish Society of Radio Amateurs, an amateur radio organization * Singapore Scout Association, youth movement founded 1910 * Seismological Society of America, international scientific society founded1906 * Scottish Socialist Alliance, a coalition of left-wing bodies, fore-runner to the Scottish Socialist Party * Shipconstructors' and Shipwrights' Association, a former British trade union * Sainsbury's Staff Association, of Sainsbury's, UK * Sudan Studies Association, US professional asso ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Control-flow Graph
In computer science, a control-flow graph (CFG) is a representation, using graph notation, of all paths that might be traversed through a program during its execution. The control-flow graph was discovered by Frances E. Allen, who noted that Reese T. Prosser used boolean connectivity matrices for flow analysis before. The CFG is essential to many compiler optimizations and static-analysis tools. Definition In a control-flow graph each node in the graph represents a basic block, i.e. a straight-line piece of code without any jumps or jump targets; jump targets start a block, and jumps end a block. Directed edges are used to represent jumps in the control flow. There are, in most presentations, two specially designated blocks: the ''entry block'', through which control enters into the flow graph, and the ''exit block'', through which all control flow leaves. Because of its construction procedure, in a CFG, every edge A→B has the property that: : outdegree(A) > 1 or inde ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Register Allocation
In compiler optimization, register allocation is the process of assigning local automatic variables and expression results to a limited number of processor registers. Register allocation can happen over a basic block (''local register allocation''), over a whole function/ procedure (''global register allocation''), or across function boundaries traversed via call-graph (''interprocedural register allocation''). When done per function/procedure the calling convention may require insertion of save/restore around each call-site. Context Principle {, class="wikitable floatright" , + Different number of scalar registers in the most common architectures , - ! Architecture ! scope="col" , 32 bits ! scope="col" , 64 bits , - ! scope="row" , ARM , 15 , 31 , - ! scope="row" , Intel x86 , 8 , 16 , - ! scope="row" , MIPS , 32 , 32 , - ! scope="row" , POWER/PowerPC , 32 , 32 , - ! scope="row" , RISC-V , 16/32 , 32 , - ! scope="row" , SP ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strength Reduction
In compiler construction, strength reduction is a compiler optimization where expensive operations are replaced with equivalent but less expensive operations. The classic example of strength reduction converts "strong" multiplications inside a loop into "weaker" additions – something that frequently occurs in array addressing. Examples of strength reduction include: * replacing a multiplication within a loop with an addition * replacing an exponentiation within a loop with a multiplication Code analysis Most of a program's execution time is typically spent in a small section of code (called a hot spot), and that code is often inside a loop that is executed over and over. A compiler uses methods to identify loops and recognize the characteristics of register values within those loops. For strength reduction, the compiler is interested in: *Loop invariants: the values which do not change within the body of a loop. *Induction variables: the values which are being iterated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Partial-redundancy Elimination
In compiler theory, partial redundancy elimination (PRE) is a compiler optimization that eliminates expressions that are redundant on some but not necessarily all paths through a program. PRE is a form of common subexpression elimination. An expression is called partially redundant if the value computed by the expression is already available on some but not all paths through a program to that expression. An expression is fully redundant if the value computed by the expression is available on all paths through the program to that expression. PRE can eliminate partially redundant expressions by inserting the partially redundant expression on the paths that do not already compute it, thereby making the partially redundant expression fully redundant. For instance, in the following code: if (some_condition) else z = x + 4; the expression x+4 assigned to z is partially redundant because it is computed twice if some_condition is true. PRE would perform code motion on the expres ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Global Value Numbering
Value numbering is a technique of determining when two computations in a program are equivalent and eliminating one of them with a semantics-preserving optimization. Global value numbering Global value numbering (GVN) is a compiler optimization based on the static single assignment form (SSA) intermediate representation. It sometimes helps eliminate redundant code that common subexpression elimination (CSE) does not. At the same time, however, CSE may eliminate code that GVN does not, so both are often found in modern compilers. Global value numbering is distinct from local value numbering in that the value-number mappings hold across basic block boundaries as well, and different algorithms are used to compute the mappings. Global value numbering works by assigning a value number to variables and expressions. The same value number is assigned to those variables and expressions which are provably equivalent. For instance, in the following code: w := 3 x := 3 y := x + 4 z := ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dead-code Elimination
In compiler theory, dead-code elimination (also known as DCE, dead-code removal, dead-code stripping, or dead-code strip) is a compiler optimization to remove code which does not affect the program results. Removing such code has several benefits: it shrinks program size, an important consideration in some contexts, and it allows the running program to avoid executing irrelevant operations, which reduces its running time. It can also enable further optimizations by simplifying program structure. ''Dead code'' includes code that can never be executed (''unreachable code''), and code that only affects '' dead variables'' (written to, but never read again), that is, irrelevant to the program. Examples Consider the following example written in C. int foo(void) Simple analysis of the uses of values would show that the value of b after the first assignment is not used inside foo. Furthermore, b is declared as a local variable inside foo, so its value cannot be used outside foo. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
